It has long been desirable to reduce the degree of trauma caused by, and attendant risks associated with, surgical procedures. In order to further this aim, there have been a large number of technical advances in recent times to enable various surgical procedures to be carried out using minimally invasive techniques.
One particular form of treatment to have benefited from advances in minimally invasive surgical procedures is the treatment of cardiovascular diseases. Whereas in the past it would have been necessary to conduct an open procedure in order to access the heart or a portion of the venous system, minimally invasive techniques have now been developed in which a catheter-based piece of surgical equipment can be deployed to a treatment location within a patient's cardiovascular system from a remote location external to the patient. Specifically, an elongate endoluminal catheter is inserted percutaneously through an incision in a patient's skin and is then advanced transluminally through the patient's vasculature from the incision location to a treatment location. A control device, mounted at the proximal end of the surgical catheter, is used to control the equipment mounted at the distal end of the surgical catheter, which has been advanced to the treatment location, from a remote location external to the patient's body.
In one particular technique, a stent is mounted on a distal end portion of the surgical catheter in a reduced-diameter configuration. The surgical catheter includes a retractable sheath which extends along at least the distal portion of the catheter to enclose the stent and to retain the stent in the reduced-diameter configuration. When the catheter distal portion has been advanced to the treatment location, the sheath is retracted to expose the stent. The stent is then caused to expand to an increased-diameter configuration at the treatment location, so that its abluminal surface engages the vessel inner wall, and thereafter serves to maintain an open fluid passageway through the vascular treatment location. The surgical catheter is then retrieved from the patient, leaving the stent in place. Preferably the stent is a so-called self-expanding stent, typically manufactured from a shape memory alloy, such as Nitinol, and being configured to expand from the reduced diameter configuration to the increased-diameter configuration due to the memorized molecular configuration of the alloy at body temperature. When the sheath is retracted, such a stent therefore adopts the increased-diameter configuration without further intervention by the medical practitioner. Balloon-expandable stents, and other configurations, are also known, however, which require intervention by the medical practitioner to cause the stent to expand from the reduced-diameter configuration to the increased-diameter configuration.
In order to be insertable through the tortuous vasculature of a patient, from the incision location to the treatment site, a surgical catheter must be flexible transverse to its longitudinal axis. This allows the catheter to follow the narrow and twisting passageways through the patient's venous system. On the other hand, such catheters must be relatively incompressible in the lengthwise direction, so as to facilitate catheter advancement by providing a driving force to guide the catheter into the vasculature from the proximal end, and so as to resist compression during retraction of the catheter sheath when a stent is to be released. For this purpose, it is not uncommon to provide a means of reinforcing the inner tubular portion of the surgical catheter, such as by providing a coil spring along the length thereof from the proximal end to the distal portion. Such a coil spring is closely wound, with adjacent turns of the coil being substantially in contact with one another, to resist compressive forces but provides the requisite degree of flexibility transverse to the coil's central axis. A so-called stent pusher may be provided at the coil distal end, configured to engage the stent and to prevent proximal displacement of the stent when a retaining sheath is withdrawn for stent release.
The sheath provided to restrain the stent in the reduced diameter configuration may be provided so as to extend along the entire length of the surgical catheter, from the proximal end to the distal tip. On the other hand, the sheath need only be provided in a region at the distal portion of the catheter, sufficient to enclose the stent along its length, and being retractable to fully expose the stent. In either case, a sheath retraction wire may be provided by which to withdraw the sheath proximally along the catheter, thereby exposing the stent at the catheter distal end portion. Typically, as noted, the stent will be self-expanding, so as to place the sheath under a circumferential pre-tension. In order to allow the sheath to slide over the catheter, the catheter and sheath are usually constructed from low-friction materials, and provided with a lubricant or lubricious surface treatment there-between.
At the proximal end of the surgical catheter, a device is provided for retracting the sheath over the catheter. Typically, such a device includes a housing by which a medical practitioner can grip the device, and to which the catheter is rigidly connected. In particular, any reinforcing member, such as a coil spring, is attached to the device distal end by a hub, by which to hold the reinforcing member in place. A retraction wire is typically provided, attached at its distal end to one end of the catheter sheath, by which to withdraw the sheath. Typically, the retraction wire extends from the connection point with the sheath, into and through a lumen inside the catheter, to extend from the proximal end of the catheter inside the device housing. An actuator is provided, operable by the medical practitioner using the device, by which the sheath wire is retracted to withdraw the sheath and expose the distal portion of the catheter. In alternative configurations, a retraction wire is not necessitated, and the sheath may be connected directly to a portion of the actuator mechanism within the housing. In most applications, the catheter sheath is configured to be withdrawn proximally along the catheter, but distal withdrawal is not impossible. The reinforcing member serves to resist compression due to the tensile stresses in the catheter sheath and retraction wire. The resulting compressive stresses are transferred from the reinforcing member to the device via the connection hub by which they are joined.
WO 02/087470 A1 discloses a sheath retraction device for proximally withdrawing a catheter sheath. The sheath is in the form of an outer tube 16 connected at its proximal end to a slider 24 in the device housing. As the slider 24 is proximally withdrawn, the sheath is retracted. The retraction device in WO 02/087470 A1 provides two actuation mechanisms by which the sheath may be withdrawn. The first is to provide a finger engagement portion (a button) on the slider 24, by which the slider and the connected outer tube 16 may be directly proximally withdrawn by retracting the slider along slider tracks provided. The second mechanism by which the sheath may be withdrawn is actuated by a finger trigger 34. A pull wire 30 extends proximally from the slider 24 to a take-up reel 32. The take-up reel is connected to a toothed gear 35, which engages with ratchet teeth 36 of the trigger 34. When the trigger is depressed, the ratchet teeth rotate the toothed gear 35 so as to wind the pull wire 30 on the take-up reel 32, thereby retracting the slider and connected sheath proximally in the housing. Because the teeth 36 are ratchet teeth, the take-up reel may only be rotated in one direction by successive pulls of the trigger. The length of a retraction stroke possible with the device of WO 02/087470 A1 is restricted by the length of the track provided for the slider 24 in the housing.
A similar device is disclosed in WO 2007/022395. In this device, a catheter outer sheath 262 is rigidly attached to a slider block 624 in the device housing. A belt 670 is provided, connected to the slider block 624 and passing around a proximal idle pulley 638 to be connected at its other end to a take-up pulley 656. Take-up pulley 656 may be rotated by an operator via a knob 640, 650, in order to wind the belt 670 onto the reel 656. As the belt is wound onto the reel, the hub 624 is retracted so as to withdraw the outer sheath 262. As the belt is wound onto the take-up pulley 656, the winding diameter of the pulley increases, thereby reducing the mechanical advantage afforded, simultaneously increasing the degree of retraction for a given rotation of the knobs 640, 650. A lock 646 may be provided so as to inhibit rotation of the knobs 640, 650 during shipping, although explanation of the operation of this lock is not given. The length of a retraction stroke of the device is again limited by the length of the track provided for sliding the proximal hub 624 within the device housing.
Several sheath retraction devices are disclosed in WO 2005/039448 A1. In the first illustrated embodiment of FIGS. 1 to 5, a wire 160 is provided, connected to the outer tube (sheath) 130. The wire is connected to a cam 190 in the device housing. The cam is coupled to a thumbwheel 180, which may be rotated by a medical practitioner when using the device. Rotation of the thumbwheel 180 causes the wire 160 to be wound onto the surface 192 of the cam 190 so as to withdraw the outer tube 130 proximally with respect to the catheter inner tube 140. Since the radius of the cam 190 increases around the cam's surface 192, the mechanical advantage provided for retracting the outer tube 130 decreases as the wheel 180 rotates, with the degree of retraction for a given amount of rotation of the thumbwheel 180 correspondingly increasing as the thumbwheel 180 rotates. The device of WO 2005/039448 is configured to achieve only a single rotation of the thumbwheel 180, thereby limiting the retraction stroke to a distance equal to the circumference of the cam outer surface 192.
For minimally invasive surgical procedures utilizing a catheter, as with any surgical procedure, hygiene is of paramount importance. Regardless of the level of trauma caused by the surgical operation, the risks of infection must be minimized or neutralised, to ensure and aid a patient's recovery. For this reason, surgical catheter devices are usually provided with a control device already attached to the catheter's proximal end, and, in the case of a stent delivery catheter, with the stent already loaded in the catheter distal end. The surgical apparatus is typically packaged in sterile packaging, ready for use when first exposed from the packaging.
Because a surgical catheter is typically several times longer than the associated control device, the catheter is normally packaged in a rolled, folded or bent configuration, rather than in a fully elongated, straight configuration. This is enabled by the inherent flexibility of such catheters. In order to use the surgical apparatus, the catheter is straightened for insertion transluminally into a patient, and is then guided to the treatment site within a patient's vasculature. Typically, a guide-wire is provided, along which the catheter is run, to bring the distal end of the catheter to the treatment location.
Both when folding and unfolding the catheter for packaging and distribution purposes, and also when running the catheter along a guide-wire to follow a tortuous passage way, localised relative motion necessarily occurs between the catheter and the sheath. In particular, the sheath is necessary relatively inextensible in the lengthwise axial direction, to enable controlled withdrawal in use. The catheter material is typically moderately elastic, so as to provide the necessary lateral flexibility, with rigidity provided by a coil spring or other reinforcing support member as described above. As the catheter bends and flexes, localised movement between the catheter and sheath can thus occur. So that this will not result in accidental premature retraction of the sheath, the sheath distal end may be formed to extend over the end of the catheter to form an atraumatic distal tip. In other known catheters, an atraumatic tip may simply be provided on the distal end of the catheter. An element of slack or flexibility is also typically provided in the sheath retraction wire, which is itself substantially inextensible, so as to accommodate relative motion of the sheath proximal end with respect of the catheter.
The overall effect of the tolerances provided to allow such flexibility and relative motion means that when the operator comes to retract the sheath, the initial stages of sheath retraction may not deliver a controlled or expected degree of motion in the sheath, as the slack is taken up. In particular, at the initial stages of stent deployment, it is essential to have full control of the positioning and placement of the stent at the distal end of the surgical catheter device, to prevent accidental movement of the stent relative to the treatment site, which could result in an unintentional patient trauma.
There is also typically some inherent lengthwise compressive flexibility in the catheter, and some lengthwise tensile flexibility in the sheath, upon initial delivery to the treatment site, before any residual compressibility or extensibility can be taken up by proximal lengthwise tensioning of the sheath wire to place the catheter under compression along the catheter length. This initial catheter compression can produce undesirable preliminary motion at the catheter distal end as the sheath retraction device is first actuated.
Whilst prior art devices including two or more separate retraction mechanisms for delivering different mechanical advantages have been provided, so as to achieve slow initial sheath withdrawal for accurate placement of the stent distal end and fast subsequent sheath withdrawal for quickly releasing the stent when placed, no device has yet been produced to specifically account for the inherent residual tolerances and material resilience of the surgical catheter construction. It would therefore be desirable to provide a sheath withdrawal device constructed and arranged to accommodate specifically such residual tolerances and the material resilience of the surgical catheter construction.
It would also be desirable to provide indication to the user of such devices of when the sheath has been fully retracted, to ensure proper and accurate stent release and to indicate when the catheter may be retracted from the patient.
WO 2006/104143 A1 discloses a body organ expansion instrument 1 having a tubular member 5 capable of sliding in a proximal direction at the distal end of a distal tube 2. A pulling wire 6 is attached at the proximal end to a winding shaft portion 63 which retracts the wire 6 by winding wire 6 thereon. A linear member 71 is also provided to be wound onto shaft portion 63 also. The linear member is fed out from a bobbin 73, around which it is initially wound, as the linear member 71 is wound onto shaft portion 63. When linear member 71 is all fed out, the bobbin 73 is nonrotatable, thereby making rotational roller 61, which winds the shaft portion 63 to retract wire 6, incapable of further rotating. The end 71a of the linear member 71 is inserted into a slit 72 to be held on the shaft portion 63. The shaft portion 63 is, however, provided only with a single slit 72, and the length of linear member 71 must therefore be made in accordance with the length of the specific stent to be held by tubular member 5 at the distal end of distal tube 2.
It would be desirable to provide means whereby the same device, or devices having substantially identical construction, can be adapted for retracting the sheath by amounts corresponding to different lengths of stents to be released, and to provide indication of full and proper sheath retraction appropriate to the length of each stent being released.